Systems and methods for determining the number of channel estimation symbols based on the channel coherence bandwidth

ABSTRACT

Various systems and methods are provided for channel estimation. These systems and methods (a) determine a coherence bandwidth for the channel, (b) adapt the channel estimation based on the coherence bandwidth, and (c) perform channel estimation by transmitting a channel estimation symbol over a channel. In some embodiments, the channel estimation is adapted based on the coherence bandwidth. This may include selecting a number of channel estimation symbols to transmit in a packet. Additionally, the number of channel estimation symbols transmitted in a packet can be selected by increasing the number of channel estimation symbols when the coherence bandwidth of the channel is high or decreasing the number of channel estimation symbols when the coherence bandwidth of the channel is low.

RELATED APPLICATIONS

This application claims priority to, and is a continuation of U.S.application Ser. No. 12/491,782 filed Jun. 25, 2009, now U.S. Pat. No.9,100,256, and which claims priority to U.S. Provisional Application No.61/145,042, having a filing date of Jan. 15, 2009, now expired. Each ofthe above referenced documents is hereby incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

This disclosure relates to communication systems, and at least some ofthe examples disclosed herein relate more particularly to systems andmethods for determining the number of channel estimation symbols to betransmitted to estimate a channel of a communications link based on thechannel coherence bandwidth of the channel.

FIG. 1 is a diagram that illustrates an example of a wirelessenvironment. An area 100 includes various transmitting and receivingdevices 102, 104, and 106. These devices 102, 104, and 106 can includemobile phones, radio and television transmitters, wireless networkingdevices, etc. Some of the devices 102, 104, and 106 are mobile devices;some are not mobile. Mobile or not, however, the communicationenvironment in which these devices operate is constantly changing.Signals from these devices 102, 104 and 106 reflect off buildings 108,vehicles 110 and 112, hills 114 and other features of the geographicarea 100. Further, features of the area 100 are changing. Vehicles 110and 112 move, people move within the area 100, weather patterns change,new buildings are built, etc. All of these and many other factors leadto a constantly changing communications environment.

The characteristics of wired communications channels, on the other hand,tend to be more consistent, even though they may vary with temperature,equipment changes, etc. Because of this relative consistency, it can beadvantageous to estimate certain channel characteristics in ways notused in a wireless communication system, even if these wired systems usesimilar modulation techniques.

One example of a wired system is the system defined by the Multimediaover Coax Alliance (MoCA™). In a MoCA system, coaxial cables are used toconnect components of the network, such as computers, TVs, set top boxesand radios, and generally, to distribute Ethernet signals throughout ahome or building. MoCA systems are generally used to allow suchentertainment devices within a home network to communicate with oneanother and share data, including multimedia data, such as televisionshows, movies, internet data, music, video clips, etc. One advantage ofsuch MoCA systems is that new home wiring might be avoided because manyhomes already have adequate coaxial wiring installed. MoCA systems aretypically used to distribute high-quality multimedia content andhigh-speed data with throughput exceeding 100 megabit per second.

MoCA devices generally communicate with one another in the 1 GHzmicrowave band using orthogonal frequency-division multiplexing (OFDM)modulation. The OFDM modulated signals used by MoCA are communicatedover MoCA channels using frequency-division multiplexing (FDM). In MoCAsystems that use OFDM, each MoCA channel is formed from one of a largenumber of closely-spaced orthogonal sub-carriers. These MoCA channelsare typically used to carry data. Each sub-carrier is typicallymodulated with a conventional modulation scheme at a low symbol rate,maintaining total data rates similar to conventional single-carriermodulation schemes in the same bandwidth. Some example modulationsinclude quadrature amplitude modulation (QAM) or phase shift keying(PSK) modulation.

In order to take advantage of the maximum bandwidth of each channel,some systems may characterize each channel between each device and eachother device. The characteristics of each channel are determined bytransmitting an error vector magnitude (EVM) probe consisting of a fixedpattern from one device, i.e., a node in the network, to each otherdevice that serves as a node on the network. Each such receiving devicemeasures the deviation from the fixed pattern of the EVM probe in orderto determine the amount of distortion to symbols transmitted over thechannel due to gain, phase, delay and other characteristics of thechannel.

In some multi-carrier communication systems, such as OFDM systems,channel estimation is used to characterize each channel so that theeffects of variations in gain, phase and delay can be removed from theplayload in order to provide reliable decoding of data in acommunication system. Wireless communications will often experiencedifferent channel responses either in different environments or atdifferent times, or both. These changes may be due to multi-pathphenomena, for example. Channel estimation can be used to improve thequality of communications in a communication environment. Wired systemsmay also benefit from channel estimation because the channel estimationinformation can be used to characterize the wired communicationenvironment. This environment may also vary over time due to componentchanges, temperature changes, etc.

Some OFDM systems may use a pilot sub-carrier to provide channelestimation with respect to data sub-carriers. In OFDM systems there aregenerally enough pilot sub-carriers and the distribution of the pilotsub-carriers may be uniform and contiguous such that the channelresponse of the data sub-carriers can be estimated relatively accuratelyfrom a measured pilot sub-carrier channel response. Accordingly, Channelestimation may be performed using OFDM symbols where some subset ofsubcarriers is used for channel estimation and the remaining subset ofsubcarriers is used for data. The subset of subcarriers used for channelestimation may change from OFDM symbol to OFDM symbol. OFDM symbolswhich consist solely of channel estimation subcarriers are calledchannel estimation symbols. In some OFDM systems such as MOCA systems, acomplete OFDM symbol (a symbol that is transmitted on all sub-carriers)is transmitted to estimate the channel. Such symbols are called channelestimation symbols. Some protocols, such as MoCA 1.0, mandate that everypacket start with exactly two channel estimation symbols. Since channelestimation symbols take up bandwidth, there is a need for a method andapparatus that can reduce the number of channel estimation symbols andthus increase the data throughput over the network.

BRIEF SUMMARY OF THE INVENTION

Various embodiments of systems and methods for determining the number ofchannel estimation symbols to use are presented. Some embodiments of thedisclosed method and apparatus are directed toward systems and methodsthat (a) determine a coherence bandwidth for the channel, (b) adapt thechannel estimation based on the coherence bandwidth, and (c) performchannel estimation by transmitting a channel estimation symbol over achannel. However, always using two channel estimation symbols inchannels with high coherence bandwidth is inefficient. That is, whenthere is high coherence bandwidth, it may not require two channelestimation symbols to estimate the channel. If those channel estimationsymbols were not needed then data can be sent instead.

Determining the minimum number of channel estimation symbols that shouldbe sent for a particular channel using a particular communication systemmay improve data throughput. In an OFDM or other communication system,the coherence bandwidth is a statistical measurement of the range offrequencies over which the channel can be considered “flat.” A flatchannel is one over which two frequencies of a signal are likely toexperience comparable or correlated amplitude fading. Frequencies thatlie within the same coherence bandwidth as one another tend to all fadein a similar or correlated fashion. Accordingly, when fading occurs itoccurs only over a relatively small fraction of the total signalbandwidth. The portion of the signal bandwidth over which fading doesnot occur typically contains enough signal power to sustain reliablecommunications.

In some embodiments, the channel estimation is performed by determiningthe channel coherence bandwidth and then sending channel estimationsymbols, the number of which is determined based on the coherencebandwidth. In some embodiments, this is done by decreasing the number ofchannel estimation symbols when the coherence bandwidth of the channelis high and increasing the number of channel estimation symbols when thecoherence bandwidth of the channel is low.

In one embodiment, the channel estimation is adapted based on thecoherence bandwidth by selecting between transmitting either one or twochannel estimation symbols based on the coherence bandwidth. The cyclicprefix length is indicative of the coherence bandwidth and may bedetermined based on channel profiling. In some embodiments, one channelestimation symbol is used when the cyclic prefix length is less than orequal to ⅛ of a symbol length for a symbol used and two channelestimation symbols are used when the cyclic prefix length is greaterthan ⅛ of the symbol length for the symbol used.

It will be understood, however, that different symbol length cut-offsmay be used in other embodiments. For example, 1/16 or ¼ of a symbollength might be used to determine when to transition between one and twochannel estimation symbols. In some embodiments, more than two channelestimation symbols might be used for packet transmission. The number ofchannel estimation symbols transmitted may be decreased when coherencebandwidth is high and increased when the coherence bandwidth of thechannel is low.

The larger the coherence bandwidth, the more correlated the channeleffects between adjacent subcarriers will be. If for two subcarriers,the channel is completely correlated (100% correlated), then the channelfor those two subcarriers is identical and channel estimates performedon each subcarrier can be averaged to remove estimation noise. If forthose two subcarriers, the channel is completely uncorrelated (0%correlated), then the channel for those two subcarriers will becompletely independent and thus no averaging can be performed. For someOFDM systems, there is typically considerable correlation betweenadjacent subcarriers. This correlation diminishes for second-adjacentsubcarriers and goes to zero for subcarriers separated by relativelylarge distances in frequency. This is equivalent to a weighted averageover frequency.

Other features and aspects of the disclosed method and apparatus willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the features in accordance with embodiments. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The disclosed method and apparatus, in accordance with one or morevarious embodiments, is described in detail with reference to thefollowing figures. The drawings merely depict examples of embodiments.These drawings are provided to facilitate the reader's understanding ofthe disclosed method and apparatus and should not be considered limitingof the breadth, scope of the claimed invention. It should be noted thatfor clarity and ease of illustration these drawings are not necessarilymade to scale.

FIG. 1 is a diagram that illustrates an example wireless environment.

FIG. 2 illustrates an example wired environment for an entertainmentnetwork in accordance with the systems and methods described herein.

FIG. 3 is a flow chart illustrating an example method in accordance withthe systems and methods described herein.

FIG. 4 illustrates an example channel in accordance with the systems andmethods described herein.

FIG. 5 illustrates an example packet structure in accordance with thesystems and methods described herein.

FIG. 6 is a block diagram illustrating an example computing module inaccordance with the systems and methods described herein.

The figures are not intended to be exhaustive or to limit the disclosedmethod and apparatus to the precise form disclosed. It should beunderstood that the disclosed method and apparatus can be practiced withmodification and alteration. The claimed invention should be definedonly by the claims and the equivalents thereof.

DETAILED DESCRIPTION OF THE INVENTION

Systems and methods for determining the number of channel estimationsymbols based on the channel coherence bandwidth are disclosed. WhileMoCA using OFDM is presented as an example system below, it will beunderstood by those of skill in the art that other wired communicationor slowly varying wireless communications systems may also use thedisclosed method and apparatus.

FIG. 2 illustrates an example entertainment network 202 that mightincorporate a communication system in accordance with the systems andmethods described herein. The entertainment network 202 is located in atypical family home 200. However, it will be understood that the systemsand methods described herein can be applied to various other types ofbuildings or outdoor locations that might use communication networks,such as, but not limited to, the entertainment network 202 illustratedin FIG. 2.

The home 200 is provided with entertainment services through aconnection 204 with an entertainment service provider. This connectionmay be a wired or wireless connection such as cable, satellite, fiberoptic, or other communication connection and can include internetservice, television programming, etc.

In some embodiments, connection 204 supports the communication ofcontent associated with multiple data services from multiple serviceproviders. For example, a homeowner might use satellite receivers forreceiving television content and Digital Subscribers Line (DSL) serviceto receive internet service. These services might all be connected to anetwork device 206 that then provides these services to people in thehome 200 over a wired home network 208. The wired network might usetypical computer network wiring or other types of wiring. For example,the home network 208 might use Ethernet cabling or coaxial cable with anetwork defined by a communication standard, such as MoCA 1.0. A MoCA orsimilar network is easy to set up in homes 200 in which adequate coaxialcables have been previously installed.

In some examples, telephone services are provided using a connection204. These services are then routed throughout the home 200 over thewired network 208. Alternatively, these telephone services are connectedfrom the network device 206 to a separate telephone system (not shown)within the home 200. As will be understood by those skilled in the art,many different combinations of services that use the connection 204 andmethods of distribution within the home 200 are possible with thedisclosed embodiments.

In one embodiment, the network device 206 is a network controller. Insuch an embodiment, the controller 206 provides control functionalityfor the network 208. This network 208 is a MoCA network in someembodiments. In the example network 208, internet services andtelevision services are provided through the network 208. As illustratedin FIG. 2, the network 208 is connected to network devices 210, 212 and216. In one embodiment, the network devices 210 and 212 are set topboxes that provide television programming content that can be viewedusing the televisions 218 and 220. The network device 216 provides acomputer network connection 226 to a personal computer 228. For example,a personal computer 228 is connected to the internet using the networkdevice 216. In some embodiments, the network device 216 can also includea wireless component, such as 802.11.80, to which other computers canconnect, e.g., over the internet.

Channel characteristics can be determined for the network 208 bytransmitting an EVM probe packet to a receiving device at the other endof the channel. The channel characteristics are determined using the EVMprobe packet. One such channel characteristic that can be directlymeasured is the coherence bandwidth. However, an alternative method isto measure the delay spread of the channel. The delay spread isinversely proportional to the coherence bandwidth. The delay spread is ameasure of the length of the impulse response of the channel. The longerthe impulse response of the channel, the smaller the coherencebandwidth.

In some embodiments, the delay spread is measured to determine thelength of a cyclic prefix to be added between data symbols. Cyclicprefix length is the number of bits that are added between symbols toensure that there is no intersymbol interference due to delay spreadover the channel. Delay spread may be determined based on the responseof the channel to the EVM probes. Coherence bandwidth is inverselyproportional to delay spread.

As discussed above, the coherence bandwidth is a statistical measurementof the range of frequencies over which the channel can be considered“flat.” A flat channel is one for which the frequencies of the channelare likely to experience comparable or correlated amplitude fading.Frequencies within the same coherence bandwidth tend to all fade in asimilar or correlated fashion. If the coherence bandwidth is relativelynarrow with respect to the total signal bandwidth, then when fadingoccurs it occurs only over a relatively small fraction of the totalsignal bandwidth.

If the coherence bandwidth is large, then the variations betweenadjacent sub-carriers will be small. On the other hand, if the coherencebandwidth is small, then the variations between adjacent sub-carrierswill be large. In accordance with the disclosed method and apparatus,for OFMD systems, a relatively large coherence bandwidth can beexploited to improve the channel estimate by averaging over sub-carriersthat are close in frequency. By averaging over sub-carriers that areclose in frequency, averaging over time between channel estimationsymbols can be reduced or eliminated without any degradation in theestimate. The reason for this will become clear below.

FIG. 3 is a flow chart illustrating one example of a method inaccordance with the systems and methods described herein. In step 302,the coherence bandwidth of the channel is determined. In step 304,channel estimation is performed by selecting the number of channelestimation symbols based on the coherence bandwidth. The channelestimator can average out noise between sub-carriers in the channelbetter for channels with higher coherence bandwidth and not as well forchannels with lower coherence bandwidth. For channels with lowercoherence bandwidth, multiple channel estimation symbols may be neededso that averaging can be done over time, rather than over frequency(i.e., across multiple sub-carriers). Accordingly, in one embodiment,when multiple channel estimation symbols are transmitted, time averagingcan be used to assist in estimating channel response. However, forchannels with higher coherence bandwidth, fewer channel estimationsymbols are typically required since averaging can be done overfrequency. For example, in some embodiments, a decision is made as towhether to use one or two channel estimation symbols based upon therelative length of the cyclic profile with respect to the OFDM symbollength.

In one embodiment of the disclosed method and apparatus, the cyclicprefix length is indicative of the coherence bandwidth and may bedetermined based on channel profiling. In one such embodiment, when thelength of the cyclic profile is less than ⅛ of OFDM symbol length, thenone channel estimation symbol is used. Otherwise, two channel estimationsymbols are used. It should be understood that in addition to reducingthe number of channel estimation symbols, the number of channelestimation sub-carriers (i.e., subcarriers dedicated to channelestimation) can also be reduced.

When a channel estimation symbol is transmitted, that symbol cannot beused to transmit other data. Accordingly, decreasing the number ofchannel estimation symbols in a communication system is typicallydesirable. On the other hand, however, channel estimation symbolsperform an important function in allowing a communication system toperform channel estimation. In some multi-carrier communication systems,such as OFDM systems, channel estimation is used to characterize eachchannel so that the channels might provide reliable decoding of data ina communication system. Wireless communications will often experiencedifferent channel responses either in different environments or atdifferent times, or both. These changes may be due to multi-path fading,for example. Channel estimation can be used to improve the quality ofcommunications in a communication environment. Wired systems may alsobenefit from channel estimation because the channel estimationinformation can be used to characterize the wired communicationenvironment. This environment may also vary over time due to componentchanges, temperature changes, etc.

In step 306, channel estimation is performed. The channel estimation canbe performed by, for example, transmitting a channel estimation symbolas part of a communication packet. One or more channel estimationsymbols may be transmitted. In some cases, limiting the number ofchannel estimation symbols improves throughput by allowing more datasymbols to be transmitted in the place of the eliminated channelestimation symbols.

FIG. 4 is a diagram illustrating an example channel 400 in accordancewith the systems and methods described herein. The channel 400 is brokeninto N sub-carriers. The sub-carriers may be used to transmit data. Forexample, some embodiments use an OFDM system made up of a number ofsub-carriers to transmit data from one OFDM device to another. Thesetransmissions may be wireless or wired transmissions, depending on therequirements of the particular system involved.

In OFDM, the sub-carrier frequencies may be chosen so that thesub-carriers are orthogonal to each other. If the sub-carriers areorthogonal, cross-talk between the sub-carriers may be decreased suchthat inter-carrier guard bands are not used. Eliminating inter-carrierguard bands can simplify the design of OFDM transmitters and thereceivers because separate filters for each sub-carrier may not berequired.

The packets transmitted may include one or more channel estimationsymbols. The number of channel estimation symbols used can vary from onechannel to another. Some channels may use one channel estimation symbol,while other channels use two or more.

FIG. 5 is a diagram illustrating an example packet structure 500 inaccordance with the systems and methods described herein. The packet500, in the illustrated example, includes a timing sequence 502. Thetiming sequence 502 may be used to synchronize transmissions so that thebeginning and ending of symbols can be accurately determined by thereceiving device.

The packet 500 also includes a guard interval 504. The long duration ofeach symbol makes it practical to use such guard intervals 504, 508,512, and 516. The guard intervals 504, 508, 512, and 516 are insertedbetween the OFDM symbols. This decreases intersymbol interference. Insome embodiments, the guard intervals 504, 508, 512, and 516 eliminatethe need for a pulse-shaping filter, reduce the sensitivity to timesynchronization problems, or both.

In some embodiments, the guard intervals 504, 508, 512, and 516 are acyclic prefix. The cyclic prefix is at the beginning of an OFDM symbol.Alternatively, the cyclic prefix can be located at the end. In oneembodiment, a portion of the OFDM symbol used is transmitted during theguard interval 504, 508, 512, and 516 and is followed by the OFDMsymbol. Transmitting a portion of an OFDM symbol during the guardinterval allows the receiver to integrate over an integer number ofsinusoid cycles for each of the multipaths when it performs OFDMdemodulation with the Fast Fourier Transform (FFT).

The packet 500 also includes a channel estimation portion 506. In oneembodiment, the channel estimation portion 506 includes one or morechannel estimation symbols. The number of channel estimation symbolsvaries from one packet to another based on the systems and methodsdescribed herein. In one example, channels with low coherence bandwidthuse multiple channel estimation symbols, while channels with highcoherence bandwidth use fewer or a single channel estimation symbol. Inthis way, throughput may be increased in some cases.

In some embodiments, a system selects between transmitting one or twochannel estimation symbols. The selection can be made based on, forexample, the cyclic prefix length. The cyclic prefix length isindicative of the coherence bandwidth and may be determined based onchannel profiling.

In some embodiments, if the cyclic prefix length is less than ⅛ of theOFDM symbol length, then only one channel estimation symbol is used. Ifthe cyclic prefix length is greater than ⅛ of the OFDM symbol length,then two channel estimation symbols may be used. (Generally, many OFDMsystems limit the cyclic prefix length to a maximum of ¼ of the OFDMsymbol length.) For short packets, e.g., a single symbol unicast packet,which may include approximately 480+ data bytes, the channel estimationoverhead is about 62% of the packet when two channel estimation symbolsare used and 47% when one channel estimation symbol is used. Thissavings of 25% improves throughput.

The packet 500 also includes data portions 510, 514, and 518. These dataportions 510, 514, and 518 can include data symbols. The data symbolsmay be, for example, user data that is transmitted from onecommunication device to another.

A Computing module 600 might also include a communications interface624. The Communications interface 624 might be used to allow softwareand data to be transferred between the computing module 600 and externaldevices. Examples of a communications interface 624 might include amodem or soft-modem, a network interface (such as an Ethernet, networkinterface card, WiMedia, IEEE 802.XX or other interface), acommunications port (such as for example, a USB port, IR port, RS232port Bluetooth® interface, or other port), or other communicationsinterface. Software and data transferred via the communicationsinterface 624 might typically be carried on signals, which can beelectronic, electromagnetic (which includes optical) or other signalscapable of being exchanged by a given communications interface 624.These signals might be provided to the communications interface 624 viaa channel 628. This channel 628 might carry signals and might beimplemented using a wired or wireless communication medium. Thesesignals can deliver the software and data from memory or other storagemedium in one computing system to memory or other storage medium in thecomputing system 600. Some examples of a channel might include a phoneline, a cellular link, an RF link, an optical link, a network interface,a local or wide area network, and other wired or wireless communicationschannels.

In a multi-channel system, (perhaps better thought of as amulti-sub-channel system) a channel estimation symbol may be transmittedon one or more of the sub-channels that make up the communicationchannel. The number of channel estimation symbols transmitted can bebased on the coherence bandwidth.

In this document, the terms “computer program medium” and “computerusable medium” are used to generally refer to physical storage mediasuch as, for example, memory 608, a storage unit 620, and media 614.These and other various forms of computer program media or computerusable media may be involved in storing one or more sequences of one ormore instructions to a processing device for execution. Suchinstructions embodied on the medium, are generally referred to as“computer program code” or a “computer program product” (which may begrouped in the form of computer programs or other groupings). Whenexecuted, such instructions might enable the computing module 600 toperform features or functions of the present invention as discussedherein

While various embodiments of the disclosed method and apparatus havebeen described above, it should be understood that they have beenpresented by way of example only, and should not limit the scope of theclaimed invention. Likewise, the various diagrams may depict an examplearchitectural or other configuration for the disclosed method andapparatus, which is done to aid in understanding the features andfunctionality that can be included. The claimed invention is notrestricted to the illustrated example architectures or configurations,but the desired features can be implemented using a variety ofalternative architectures and configurations. Indeed, it will beapparent to one of skill in the art how alternative functional, logicalor physical partitioning and configurations can be implemented toimplement the desired features. Also, a multitude of differentconstituent module names other than those depicted herein can be appliedto the various partitions. Additionally, with regard to flow diagrams,operational descriptions and method claims, the order in which the stepsare presented herein shall not mandate that various embodiments beimplemented to perform the recited functionality in the same orderunless the context dictates otherwise.

Although the disclosed method and apparatus is described using variousembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more of the otherdisclosed embodiments, whether or not such embodiments are described toinclude that feature. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-describedembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is: 1-18. (canceled)
 19. A method comprising:determining, by a wireless receiver, a cyclic prefix length of a signalreceived over a wireless channel; and generating, by the wirelessreceiver, a channel estimate of the wireless channel, wherein the numberof symbols in the channel estimate is based on the cyclic prefix length.20. The method of claim 19, comprising: determining, by the wirelessreceiver, to include a lower number of channel estimation symbols whenthe cyclic prefix length is less than ⅛ of a symbol length; anddetermining, by the wireless receiver, to include a higher number ofchannel estimation symbols in the packet when the cyclic prefix lengthis greater than ⅛ of the symbol length.
 21. The method of claim 20,wherein the higher number of symbols corresponds to a smaller coherencebandwidth and the lower number of symbols corresponds to a largercoherence bandwidth.
 22. The method of claim 20, wherein the smallernumber of symbols is one and the larger number of symbols is two. 23.The method of claim 19, comprising estimating a coherence bandwidth, bythe wireless receiver, to determine the cyclic prefix length.
 24. Themethod of claim 19, comprising channel profiling, by the wirelessreceiver, to determine the cyclic prefix length.
 25. A methodcomprising: estimating, by the wireless receiver, one or morecharacteristics of a signal communicated on a channel, wherein the oneor more characteristics comprise cyclic prefix length of the signal andare indicative of a coherency bandwidth of the channel; determining,based on the one or more characteristics, whether one or two channelestimation symbols are included in a channel estimate; including onechannel estimation symbol in the channel estimate when the cyclic prefixlength is less than ⅛ of a symbol length; and including two channelestimation symbols in the channel estimate when the cyclic prefix lengthis greater than ⅛ of the symbol length.
 26. The method of claim 25,wherein the wireless receiver is configured to: include two channelestimation symbols in the channel estimate when the one or morecharacteristics are indicative of the channel having a smaller coherencebandwidth; and include one channel estimation symbol in the channelestimate when the one or more characteristics are indicative of thechannel having a larger coherence bandwidth.
 27. The method of claim 25,wherein the wireless receiver is configured to perform channel profilingto determine the cyclic prefix length.
 28. The method of claim 25,wherein the method comprises communicating the channel estimate in apacket.
 29. A wireless communication device comprising: a wirelessreceiver operable to determine a cyclic prefix length of a signalreceived over a wireless channel and generate a channel estimate of thewireless channel, wherein the number of symbols in the channel estimateis based on the cyclic prefix length; and a wireless transmitteroperable to communicate the channel estimate in a data packet.
 30. Thewireless communication device of claim 29, wherein the wireless receiveris operable to include a lower number of channel estimation symbols inthe channel estimate when the cyclic prefix length is less than ⅛ of asymbol length, and wherein the wireless receiver is operable to includea higher number of channel estimation symbols in the packet when thecyclic prefix length is greater than ⅛ of the symbol length.
 31. Thewireless communication device of claim 30, wherein the higher number ofsymbols corresponds to a smaller coherence bandwidth and the lowernumber of symbols corresponds to a larger coherence bandwidth.
 32. Thewireless communication device of claim 30, wherein the smaller number ofsymbols is one and the larger number of symbols is two.
 33. The wirelesscommunication device of claim 29, wherein the wireless receiver isoperable to estimate a coherence bandwidth to determine the cyclicprefix length.
 34. The wireless communication device of claim 29,wherein the wireless receiver is operable to perform channel profilingto determine the cyclic prefix length.
 35. A wireless communicationdevice comprising: a wireless receiver operable to estimate one or morecharacteristics of a signal communicated on a channel, wherein the oneor more characteristics comprise cyclic prefix length of the signal andare indicative of a coherency bandwidth of the channel, and wherein thewireless receiver operable to generate a one-symbol channel estimatewhen the cyclic prefix length is less than ⅛ of a symbol length and atwo-symbol channel estimate when the cyclic prefix length is greaterthan ⅛ of the symbol length.
 36. The wireless communication device ofclaim 35, wherein the wireless receiver is configured to generate theone-symbol channel estimate when the one or more characteristics areindicative of the channel having a smaller coherence bandwidth and thetwo-symbol channel estimate when the one or more characteristics areindicative of the channel having a larger coherence bandwidth.
 37. Thewireless communication device of claim 35, wherein the wireless receiveris configured to perform channel profiling to determine the cyclicprefix length.
 38. The wireless communication device of claim 35,wherein the wireless communication device comprises a wirelesstransmitter operable to communicate the channel estimate in a datapacket.